Mens Rea, or “guilty mind,” marks a central distinguishing feature of criminal law. An injury caused without mens rea might be grounds for civil liability but typically not for criminal. Criminal liability requires not only causing a prohibited harm or evil -- the “actus reus” of an offense -- but also a particular state of mind with regard to causing that harm or evil. For a phrase so central to criminal law, “mens rea” suffers from a surprising degree of confusion in its meaning. One source of confusion arises from the two distinct ways in which the phrase is used, in a broad sense and in a narrow sense. In its broad sense, “mens rea” is synonymous with a person’s blameworthiness, or more precisely, those conditions that make a person’s violation sufficiently blameworthy to merit the condemnation of criminal conviction. In this broad sense, the phrase includes all criminal law doctrines of blameworthiness -- mental requirements of an offense as well as excuse defenses such as insanity, immaturity, and duress, to name a few. This was a frequent usage of “mens rea” at common law. It remains common among nonlegal disciplines such as philosophy and psychology, perhaps because it captures in a single phrase criminal law’s focus on personal culpability. The modern meaning of mens rea, and the one common in legal usage today, is more narrow: Mens rea describes the state of mind or inattention that, together with its accompanying conduct, the criminal law defines as an offense. In more technical terms, the mens rea of an offense consists of those elements of the offense definition that describe the required mental state of the defendant at the time of the offense, but does not include excuse defenses or other doctrines outside the offense definition. To help distinguish this more narrow conception from the broader, the Model Penal Code drafters substitute the term “culpability” for “mens rea.” Thus, Model Penal Code section 2.02, governing the Code’s offense mental states, is titled “General Requirements of Culpability” and subsection (2), defining the offense mental elements employed by the Code, is titled “Kinds of Culpability.” Unfortunately, the term “culpability” has come to suffer some of the same confusion between broad and narrow meanings as the term “mens rea.” While most frequently used in its narrow sense, as interchangeable with “offense mental elements,” “culpability” is sometimes used in a broad sense, as interchangeable with “blameworthiness.” The meaning of both “mens rea” and “culpability” must often be determined from their context. Available for download at http://ssrn.com/abstract=661161
Robinson, Paul H., "Mens Rea" (2002). Faculty Scholarship at Penn Law. 34.